This invention relates to guitars, and deals more particularly with a guitar of the type having a hollow body portion or sound box which cooperates with the sound board portion so as to amplify the fundamental source of sound, namely the vibration of the strings, in order to provide the desired integration of sound produced by the instrument.
Conventional guitar construction techniques call for use of a relatively thin planar sound board, usually of wood, mounted to a somewhat heavier box or bowl. The bowl may be fabricated from fiberglass as shown, for example, in my prior U.S. Pat. No. 3,656,395 issued Apr. 18, 1972. The wood sound board in such a guitar is usually on the order of 0.10 to 0.12 inches in thickness, and it has been found that this dimension leads to desirable tonal qualities in a guitar construction having the necessary strength in the sound board portion of the instrument to support its taut strings. The strings transmit sound vibrations to the sound board through a bridge mounted to the front face of the sound board, and the tension forces in these strings are such that the thin sound board is usually internally braced so as to react such forces. Further, a sound opening must also be provided in the sound board to allow the air contained inside the instrument to be pulsed by the vibrating strings and sound board, and thereby amplified. Thus, the hollow sound box or bowl acts in the nature of an organ pipe in carrying out this function, and the sound produced by a guitar is an integration of the contributions made by the strings, the sound board itself, and the pulsed air in this chamber.
Still with reference to conventional guitar construction techniques, the sound opening is most often located between the bridge and the lower end of the guitar neck portion and more particularly the fret board. Thus, the opening is generally provided in centered relationship on the longitudinal axis of the instrument, and hence is located directly behind the strings themselves. This location for the sound opening has an undesireable effect from the point of view of structural considerations, in that it reduces the sound board's strength in the stress path which reacts the tension forces in the strings, and moments created thereby. As a result of this location for the sound openings, present day guitars usually include rather extensive cross bracing both above and below the sound opening in order to permit the sound board to accommodate the above mentioned stresses in stress paths located on either side of the single sound opening. While additional bracing is often utilized to vary the response characteristic of the sound board with respect to the wide range of frequencies characteristic of guitars generally, it is noted that the rather extensive cross bracing characteristic of present day guitars, especially that bracing located adjacent the sound opening, is in fact necessary for the reacting of these tension forces and moments arising from these tension forces in the strings.
A general object of the present invention, therefore, is to provide a sound board in which the sound opening is relocated in order to obviate the need for such extensive cross bracing, and to permit a larger portion of the sound board itself to be devoted to the achievement of a desired vibration pattern which is related primarily to the acoustic response characteristics of the instrument rather than by structural considerations with respect to reacting the forces of the strings upon this portion of the instrument.